Basal cellular alterations of esterase, glutathione, glutathione S-transferase, intracellular calcium, and membrane potentials in coumaphos-resistant Boophilus microplus (Acari: Ixodidae) cell lines

Organophosphate (OP) acaricide resistance in Boophilus microplus ticks compromises the efficacy of tick control programs. Mechanisms that may contribute to acaricide resistance were evaluated by partial characterization of three OP-resistant B. microplus tick cell lines (C34, C44, and C54) compared to nonresistant control cells, The resistant cells showed an increase in glutathione coupled with a decrease in glutathione S-transferase activity, decreased plasma and mitochondrial membrane potentials, increased intracellular calcium concentration, and increased esterase levels. These results are consistent with resistance mechanisms found in other cell systems and with in vivo observations of increased esterase activity in organophosphate-resistant ticks. No significant differences were found in intracellular pH, drug efflux, or reactive oxygen species. The use of organophosphate-resistant cell lines offers a convenient vehicle for studying mechanisms of acaricide resistance development in vitro. (C) 2002 Elsevier Science (USA).